Nonreciprocity in Acoustic Circulator

Dr. Andrea Alù, along with graduate students Romain Fleury, Caleb F. Sieck, Postdoctoral Associate Dimitrios L. Sounas, and Research Scientist Michael R. Haberman, developed the first-of-its-kind circulator for sound, which breaks time-reversal symmetry for acoustic waves. 

Acoustic isolation and nonreciprocal sound transmission are highly desirable in many practical scenarios. They may be realized with nonlinear or magneto-acoustic effects, but only at the price of high power levels and impractically large volumes. In contrast, nonreciprocal electromagnetic propagation is commonly achieved based on the Zeeman effect, or modal splitting in ferromagnetic atoms induced by a magnetic bias. Here, we introduce the acoustic analog of this phenomenon in a subwavelength meta-atom consisting of a resonant ring cavity biased by a circulating fluid. The resulting angular momentum bias splits the ring’s azimuthal resonant modes, producing giant acoustic nonreciprocity in a compact device. We applied this concept to build a linear, magnetic-free circulator for airborne sound waves, observing up to 40-decibel nonreciprocal isolation at audible frequencies.

Read the full paper here: Sound Isolation and Giant Linear Nonreciprocity in a Compact Acoustic Circulator